The present invention relates to a method for checking the transfer of data cells in an asynchronous switching arrangement and more specifically for detecting transfer errors of data cells due to unacceptable delays and unwanted copying. It also relates to switching units equipped for such a check.
Information transfer in an asynchronous switching network by means of data cells is disturbed when excessive delays or losses of data cells happen, such drawbacks being linked for instance to internal queuing for a switching unit in a switching arrangement.
Occurrence of such unacceptable delays at the level of a switching arrangement, for instance in an elementary switching unit, for the smallest or in a switching network for the biggest, is usually checked by measurements carried out at the edges of the switching arrangement. Localization of a faulty element, for instance a faulty buffer or a faulty switching device requires generation of dedicated test traffic and corresponding measurements. Use of dedicated test traffic connections is known for connection oriented switches, putting out of service a part of a switch is usually carried out with multi-path switches. All this usually requires specialized technicians with appropriate testing equipment and is sometimes long and costly, for instance when there are sporadic, pattern related malfunctions which are hard to reproduce on will, and consequently to localize.
Accordingly and as much as possible, test traffic for a detection in a large switching arrangement is usually limited in time and/or to a part fraction of the traffic which is transferred, for instance less than 1% of the total traffic. Obtention of a global detection picture, if possible, and localization of a faulty element are rather long tasks and accordingly they are not as efficient as needed.
An object of this invention, therefore, is to provide a method for checking the transfer of data cells in an asynchronous switching arrangement.
According to the invention, the method comprises a marking and a counting of the cells received and a counting of the cells, after switching when outputted from the switching structure of the arrangement, in order to verify that the counts correspond and to find transfer errors of data cells due to unacceptable delays and unwanted copying in the switching structure, said marking and said counting being obtained according to a periodical time frame made of interleaved checking cycles which are grouped by limited and successive series of a same determined number of cycles, each cycle including a first phase for marking and counting the cells as they are received, the identification mark, introduced in every cell received during this first phase, being related to the position of the cycle among the other cycles of the same series, with each first phase of a cycle following immediately the first phase of the preceding cycle, a second phase, overlapping with the first phase, starting with a determined delay which may be zero, after the beginning of the first phase of the same cycle and during this first phase, for a determined duration and for counting the cells, as soon as switched, which contain the identification mark introduced during the first phase of the same checking cycle, a determination being made at the end of the second phase of each checking cycle of the correspondence between the two counts obtained during the cycle, with a specific signaling as soon as the correspondence as otherwise determined for a cycle is not obtained.
Another object of this invention is to provide an elementary asynchronous switching unit including at least one asynchronous switching arrangement provided with means for checking the transfer of data cells in this elementary unit.
Another object of the invention is to provide an asynchronous switching network or sub-network including inter-linked switching units in one or several asynchronous switching arrangement(s), with each arrangement provided with means for checking the transfer of data cells in this elementary unit.
It should be noticed that the term ‘comprising’, used in the claims, should not be interpreted as being limitative to the means listed thereafter. Thus, the scope of the expression ‘a device comprising A and B’ should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.